A number of organophosphorus compounds are used as pesticides and nerve agents. For example, organophosphorus-based pesticides, including paraoxon, parathion and diazinon are widely used in the agriculture industry and the resultant environmental pollution is well documented. Because of their toxicity and relatively high solubility in water, organophosphorus-based pesticides pose a clear threat to drinking water and aquatic life. It is therefore necessary to monitor the levels of these materials in industrial waste waters, agricultural runoffs, and other environments to determine compliance with federal and state regulations and other safety guidelines, as well as efficiency of wastewater treatments.
In addition, organophosphorus-based nerve gases, including the chemically similar organo-fluorophosphorus compounds, sarin and soman, are of particular concern due to the increasing incidence of terrorism. Recent experiences such as the subway bombing in Japan have shown that the production of nerve agents by terrorists is a relatively simple process. Further, the use of nerve agents on troops in the Iran-Iraq war, operation Desert Stomm, coupled with concerns over the possible leakage of aging stockpiles of chemical weapons, have prompted the desire for small portable devices that can be used for real time monitoring of these substances.
The detection and quantification of these highly toxic compounds by remote sensors at very low levels in the surrounding environment are critical during their production, storage, transportation, and decontamination processes. A variety of techniques have been studied based on physical, chemical and biological approaches, but currently, there are few small and inexpensive sensors with the capability to do real time monitoring/detecting of these compounds or other atmospheric gases of military or environmental concern. Methods for the unambiguous detection and quantitation of specific gaseous species usually involve separate sampling and analysis steps using complex and expensive devices such as gas chromatography with detection by either flame ionization or mass spectrometry. Much of the technology being used, such as gas chromatography-mass spectroscopy (GC-MS) and high performance liquid chromatography (HPLC), are large (not portable), expensive or require sophisticated, often extensive analysis procedures making them undesirable for real-time field analysis.
Optical sensors for the detection of analytes generally rely on small changes in the indices of refraction in response to the presence of an analyte. Commonly used optical sensors include planar waveguides, optical fibers, metallized prisms and diffraction gratings. These and other conventional methods typically require extensive analysis procedures that can take up to 24 hours to perform. Although all these techniques have some degree of sensitivity, they lack specificity, simplicity, rapid detection and portability.
Surface acoustic wave (SAW) devices/sensors typically comprise piezoelectric crystals that detect the mass of chemical vapors absorbed into the chemically selective coating on the sensor surface. This absorption causes a change in the resonant frequency of the sensor. An internal microcomputer measures these changes and uses them to determine the presence and concentration of chemical agents. Conventional SAW sensors have coatings that exhibit unique physical properties that allow a reversible absoprtion of an analyte, such as chemical vapors. The polymer-coated sensor combined with trainable software loaded into a microcomputer to recognize chemical vapor signature patterns, completes the analysis. Although conventionally available SAW sensors meet the needs of real time analysis and offer the additional benefits of multiple gas detection capability, rugged designs, computerized control, easy operation and low cost, they typically lack selectivity, especially with respect to chemically similar organophosphorus compounds, e.g., pesticides and insecticides, thus, making false positive readings a major concern. It is therefore necessary to develop detection devices and methods that address the above and other problems.